Highly-depleted laser doped semiconductor volume

ABSTRACT

A device with increased photo-sensitivity using laser treated semiconductor as detection material is disclosed. In some embodiments, the laser treated semiconductor may be placed between and an n-type and a p-type contact or two Schottky metals. The field within the p-n junction or the Schottky metal junction may aid in depleting the laser treated semiconductor section and may be capable of separating electron hole pairs. Multiple device configurations are presented, including lateral and vertical configurations.

PRIORITY DATA

This application is a continuation of U.S. patent application Ser. No.12/782,449, filed on May 18, 2010 now U.S. Pat. No. 8,143,688, which isa continuation of U.S. patent application Ser. No. 12/362,078, filedJan. 29, 2009 now U.S. Pat. No. 7,745,901, both of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to systems and methods for configuring anenhanced photodiode with increased photosensitivity. In particular, thedisclosure relates to an enhanced photodiode using laser treatedsemiconductor as detection material that separates electron hole pairsusing an electric field generated by a variety of sources, including p-njunctions and Schottky junctions.

BACKGROUND OF THE INVENTION

The design of a sensitive photodetective element involves considerationof photon absorption, excitor or electron hole pair (EHP) generation andEHP separation. For example, the materials in a silicon p-n junction ora Schottky metal junction are generally good absorbers of visible lightradiation. That is, devices incorporating p-n junctions or Schottkymetal junctions provide high rates of photon absorption. With theabsorption of each photon, there is a probability that the absorbedphoton will generate an EHP. If the DIP is generated in the depletionregion of the junction, the applied or built in electric field willcause the EHP constituents to drift in opposite directions due to theopposing electric charge signs. If the EHP is not separated by anelectric field, the probability is increased that the electron and holewill recombine and reduce the photodetective efficiency of the device.

SUMMARY OF THE INVENTION

The doping of silicon using an ultrafast femtosecond laser has beenshown to impart effective photon absorption capabilities, extend theabsorption spectral cutoff, and decrease the optical absorptioncoefficient. Doping during laser ablation and rapid cooling may causeself forming nanocrystals comprising a combination of dopant, substrate,and impurities that allow these characteristics of laser-dopedsemiconductors. The high concentration of localized nanocrystals canform quantum confinement in the form of quantum wells or quantum dots.In these cases, the confinement of charges is discretized to certainenergy levels within the bandgap of the substrate. If the concentrationand distribution of these quantum structures is optimized, anintermediate band is formed within the bandgap and a plurality of Fermilevels (e.g., three) are defined. Structures of these types can decreasethe optical absorption coefficient and extend the optical cutoffwavelength of a photodetector. A device designed to optimize theefficient collection of EHPs in such a structure may provide an electricfield to separate the positive and negative charge carriers within thedevice. Therefore, an applied field across the photodetective volumepromotes an efficient photodetector.

One or more embodiments provide a photodiode including an n-typesection, a p-type section, and a laser treated semiconductor section.The laser treated semiconductor section may be disposed between then-type section and the p-type section such that the n-type section andthe p-type section can generate an electric field substantially capableof depleting at least a portion of the laser treated semiconductorsection of free carriers and separating resulting electron-hole pairsgenerated in the laser treated semiconductor section. The laser treatedsemiconductor section may comprise a net doped n-type material and then-type section may have a higher level of n-doping than the lasertreated semiconductor section. Alternatively, the laser treatedsemiconductor section may comprise a net doped p-type material and thep-type section may have a higher level of p-doping than the lasertreated semiconductor section. The photodiode may further comprise apair of electrical contact points, one on either side of the lasertreated semiconductor section. The photodiode may further comprise asubstrate proximal to the laser treated semiconductor section and atleast a pair of electrical contact points, one proximal to a face of thelaser treated semiconductor section and the other proximal to a face ofthe substrate opposing the face of the laser treated semiconductorsection. The photodiode may also comprise a substrate proximal to thelaser treated semiconductor section and a plurality of electricalcontact points disposed proximal to a face of the laser-treatedsemiconductor section. In some embodiments, the n-type section maypartially enclose the p-type section and the laser treated semiconductorsection. Alternatively, the p-type section may partially enclose then-type section and the laser treated semiconductor section.

One or more embodiments provide a photodiode including a first Schottkycontact, a second Schottky contact, and a laser treated semiconductorsection. The laser treated semiconductor may be at least partiallydisposed between the first Schottky contact and the second Schottkycontact. The first Schottky contact may have a higher work function thanthe second Schottky contact, such that the first Schottky contact andthe second Schottky contact generate an electric field capable ofsubstantially preventing to electron-hole pairs generated by the lasertreated semiconductor section from recombining in at least some portionof the laser treated semiconductor section. The Schottky contacts maycomprise a pair of electrical contact points, one on either side of thelaser treated semiconductor section. The photodiode may further comprisea substrate proximal to the laser treated semiconductor section and theSchottky contacts comprising at least a pair of electrical contactpoints, one proximal to a face of the laser treated semiconductorsection and the other proximal to a face of the substrate opposing theface of the laser treated semiconductor section. The photodiode mayfurther comprise a substrate proximal to the laser treated semiconductorsection and the Schottky contacts providing a plurality of electricalcontact points disposed proximal to a face of the laser-treatedsemiconductor section. The first Schottky contact may partially enclosethe second Schottky contact and the laser treated semiconductor section.Alternatively, the second Schottky contact may partially enclose thefirst Schottky contact and the laser treated semiconductor section.

One or more embodiments provide a photodiode including a first dopedsection, a second doped section, and a laser treated semiconductorsection. The second doped section may be substantially bounded by thefirst doped section and the laser treated semiconductor section may besubstantially bounded by the second doped section. The photodiode mayfurther comprise a first and a second contact. The first contact may becoupled to the first doped section and the second contact may be coupledto the second doped section. The first doped section and the seconddoped section may be substantially annular and the laser treated sectionmay be substantially disk shaped. The first doped section may be n dopedand the second doped section may be p doped. Alternatively, the firstdoped section may be p doped and the second doped section may be ndoped.

One or more embodiments provide a photodiode including a first dopedsection comprising at least one subsection, a second doped sectioncomprising at least one subsection, a laser treated semiconductorsection, and a substrate comprising a first side. The laser treatedsemiconductor section, first doped section and second doped section maybe disposed on the first side of the substrate. The second doped sectionmay be substantially bounded by the first doped section and the lasertreated semiconductor section may be substantially bounded by the seconddoped section. The second doped section may comprise a first and asecond subsection. The second doped section first and second subsectionsmay be disposed on either side of the laser treated semiconductorsection. The first doped section may comprise a first and a secondsubsection. The first doped section first and second subsections may bedisposed on the opposite side of the second doped section first andsecond subsections from the laser treated semiconductor section.

One or more embodiments provide a photodiode including a first dopedsection comprising at least one subsection, a second doped sectioncomprising at least one subsection, a laser treated semiconductorsection, and a substrate comprising a first and second side. The lasertreated semiconductor section and the first doped section may bedisposed on the first side of the substrate. The second doped sectionmay be disposed on the second side of the substrate. The laser treatedsemiconductor section may be substantially bounded by the first dopedsection. The first doped section may comprise a first and a secondsubsection being disposed on either side of the laser treatedsemiconductor section.

There has thus been outlined, rather broadly, the more importantfeatures of the invention so that the detailed description thereof thatfollows may be better understood, and so that the present contributionto the art may be better appreciated. Other features of the presentinvention will become clearer from the following detailed description ofthe invention, taken with the accompanying drawings and claims, or maybe learned by the practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, reference is made to the following detailed description ofpreferred embodiments and in connection with the accompanying drawings,in which:

FIG. 1 illustrates an exemplary embodiment of a laser treatedsemiconductor diode where the laser treated semiconductor section islocated between a p-n junction;

FIG. 2 models a laser treated semiconductor section that is reversebiased in energy space to illustrate quantum confinement of a chargespecies within quantum wells and the free drift of the other species inthe depleted material;

FIG. 3 illustrates an exemplary embodiment of a laser treatedsemiconductor diode where the laser treated semiconductor section islocated between Schottky metal contacts;

FIG. 4 models a laser treated semiconductor section under bias in energyspace to illustrate quantum confinement of a charge species withinquantum wells and the free drift of the other species in the depletedmaterial;

FIG. 5 illustrates an exemplary embodiment of a laser treatedsemiconductor diode using a lateral diode configuration;

FIG. 6 illustrates an exemplary embodiment of a laser treatedsemiconductor diode using a vertical diode configuration; and

FIG. 7 illustrates another exemplary embodiment of a lateral diodeconfiguration.

The drawings will be described further in connection with the followingdetailed description. Further, these drawings are not necessarily toscale and are by way of illustration only such that dimensions andgeometries can vary from those illustrated.

DETAILED DESCRIPTION

Some or all embodiments hereof include a photodetection or photovoltaicdevice sensitive to certain electromagnetic wavelengths and formed on asemiconductor substrate. In some embodiments, the device includes aportion comprising a semiconductor material, for example silicon, whichis irradiated by a short pulse laser to create modified micro-structuredsurface morphology. The laser processing can be the same or similar tothat described in U.S. Pat. No. 7,057,256 to Carey et al., which ishereby incorporated by reference. The laser-processed semiconductor ismade to have advantageous light-absorbing properties. In some cases thistype of material has been called “black silicon” due to its visuallydarkened appearance after the laser processing and because of itsenhanced absorption of light and IR radiation compared to other forms ofsilicon, however, the present description is not limited and comprehendsother laser-treated semiconductor materials and resulting properties.

Generally, the wavelength of the irradiating laser pulse for makingblack silicon, its fluence, and pulse width can affect the morphology ofthe microstructured surface. In some embodiments, the laser fluence maybe between about 1.5 kJ/m.sup.2 and 12 kJ/m.sup.2, but can varydepending on the substrate composition. The choice of the fluence oflaser pulses irradiating a silicon wafer to generate a microstructuredlayer therein can also affect the gettering performance (capacity and/orspecificity) of a microstructured substrate. In some embodiments hereof,the laser pulse fluence is selected to be greater than about 3kJ/m.sup.2. More preferably, the fluence may be chosen to be in a rangeof about 3 kJ/m.sup.2 to about 10 kJ/m.sup.2, or a range of about 3kJ/m.sup.2 to about 8 kJ/m.sup.2.

Additionally, the laser pulse length can affect the morphology andabsorption properties of the treated silicon. Irradiation of a substrateas described herein can be done with femtosecond laser pulses orpicosecond or nanosecond pulses. Other factors that can affectmicrostructures morphology include laser polarization and laserpropagation direction relative to the irradiated surface.

In some embodiments, the laser microstructuring of a substrate isperformed in the presence of a mixture of two or more substances toaccomplish the present purposes. For example, silicon samples treated inthe presence of a mixture of SF.sub.6 and Cl.sub.2 exhibit an increasein the microstructure density at higher partial pressure of SF.sub.6.

We now turn to a description of an exemplary apparatus for detectingelectromagnetic radiation in at least a range of wavelengths of theelectromagnetic spectrum and/or for generating current or voltagethrough the absorption of photons.

FIG. 1 illustrates an exemplary embodiment of a laser treatedsemiconductor diode 100 where the laser treated semiconductor section102 is disposed between a p-section 104 and an n-section 106. The lasertreated semiconductor section 102 absorbs photons from the illumination108 and generates within the laser treated semiconductor section 102.The p-section 104 and the n-section 106 generate an electric field thataids in depleting the laser treated semiconductor section 102 of freecharge carriers and separating EHPs generated in the laser treatedsemiconductor section 102. Also, the laser treated semiconductorincludes a plurality of quantum wells 114 that can trap electrons orholes, depending on the type of laser treatment used, creatingadditional free carriers. In an embodiment where the laser treatedsemiconductor section 102 is net n-type, the n-section 106 may be moren-type doped than the laser treated semiconductor section 102. Likewise,in an embodiment where the laser treated semiconductor section 102 isnet p-type, the p-section 104 may be more p-type doped than the lasertreated semiconductor section 102. The exemplary embodiment in FIG. 1provides for a substantially uniform electric field and quantumconfinement of the electrons. In the example shown, the two junctions(n+ type 106 to laser treated semiconductor 102 junction 116 and lasertreated semiconductor 102 to p type 104 junction 118) are both reversebiased and the depletion section from each depletion section extendsinto both sides of each junction.

FIG. 2 models a laser treated semiconductor section in energy space toillustrate quantum confinement of a charge species (either electrons orholes) within quantum wells 214 and the free drift of the other speciesin the depleted material. In this example, electrons 210 are trapped inquantum wells 214 coupled to the conduction band, allowing the holes 212to freely drift. If desired, holes 212 may also be used as the trapspecies by changing the material used, in which case the electrons mayfreely drift. By trapping one species, enhanced photosensitivity isgained by the transport of many carriers of the freely drifting type. Adashed line is used to illustrate the Fermi energy

FIG. 3 illustrates an exemplary embodiment of a laser treatedsemiconductor diode 300 where the laser treated semiconductor section302 is located between a first 304 and second 306 Schottky contact. Thelaser treated semiconductor section 302 absorbs photons from theillumination 308 and generates electron-hole pairs within the lasertreated semiconductor section 302. The first Schottky contact 304 andthe second Schottky contact 306 may be engineered to create an energyhand structure that generates an electric field. The first Schottkycontact 304 and the second Schottky contact 306 may be connected to thelaser treated semiconductor section 302 to create metal semiconductorjunctions 310 and 312. The electric field generated by the energy bandstructure separates the EHPs and prevents or reduces the likelihood ofthem recombining. In an exemplary embodiment the work function of thefirst Schottky contact 304 (.PHI..sub.m1) is higher than the workfunction of the second Schottky contact 306 (.PHI..sub.m2). Theexemplary embodiment in FIG. 3 also provides for a uniform electricfield and quantum confinement of the electrons.

FIG. 4 models a laser treated semiconductor section under bias in energyspace to illustrate quantum confinement of a charge species (eitherelectrons or holes) within quantum wells 414 and the free drift of theother species in the depleted material Similar to the charge flow inFIG. 2, metal semiconductor contacts can provide charge and an electricfield across the laser doped material. In a metal semiconductorjunction, majority carriers are injected into the semiconductor. Byusing a laser doped material with minority carrier trapping in aphotodetector, a highly sensitive device may be obtained. In thisexample, the electrons 210 are trapped in the quantum wells 214,allowing the holes 212 to freely drift. A dashed line is used toillustrate the Fermi energy

FIG. 5 illustrates an exemplary embodiment of a laser treatedsemiconductor diode 500 using a lateral diode configuration. A lateraldiode has all of its connections on a single side of the device. Onebenefit to using a lateral configuration is its compatibility with thestandard CMOS process flow. In one exemplary embodiment, the n-type 504and p-type 506 layers are arranged in a substantially annular fashionaround a substantially disk shaped laser treated semiconductor section502. The n-type 504 layer may be connected to a contact 510.Alternatively, depending on the application, the laser treatedsemiconductor section 502 may be connected to a contact 510. The p-typelayer 506 may be connected to the contact 508. In the pictured exemplaryembodiment, the n-type layer 504 is connected to a contact 510 and thep-type layer 506 is connected to a contact 508 at or near the edge ofthe laser treated semiconductor section 502. The p-type layer 506substantially bounds the n-type layer 504. Additionally, the n-typelayer 504 substantially bounds the laser treated semiconductor section502. The laser treated semiconductor used in the laser treatedsemiconductor section 502 provides a decreased optical absorptioncoefficient due to a combined effect from the increased optical pathlength from the nanocrystalline nature of the surface layer and theimpurity state absorption of below band gap wavelengths. The decreasedoptical absorption coefficient allows a shallow junction device 500 toefficiently collect EHPs. In this embodiment, the electric fieldgenerated b the device extends laterally around the device, rather thaninto the depth of the laser treated semiconductor section 502. Thelateral field provides a lower overall leakage current due to fewer bulklevel defects within the substrate.

FIG. 6 illustrates an exemplary embodiment of a laser treatedsemiconductor diode 600 using a vertical diode configuration. A verticaldiode configuration has contacts (606 and 608) on both sides of thedevice. Potential benefits of the vertical diode configuration include:increased fill factor on the detection surface, stronger electricalfields between contacts resulting in increased EHP separation, greaterabsorption depth resulting in increased absorption efficiency. In oneexemplary embodiment, a laser treated semiconductor section 602 may bedisposed on a surface of a substrate 604 along with a p-doped section.The p-doped section may comprise at least one subsection (e.g., p-typecontacts 606). The laser treated semiconductor section 602 may liedisposed between the p-type contacts 606. The substrate may be n-typedoped and may include n-type contacts 608 on the opposite side of thesubstrate 604 from the laser treated semiconductor layer 602.

FIG. 7 illustrates another exemplary embodiment of a lateral diodeconfiguration. In this embodiment, a laser treated semiconductor section702 is disposed on the surface of a substrate 704 along with a p-dopedsection and an n-doped section. The p-doped section may comprise atleast one subsection (e.g., p-type contacts 706). The n-doped sectionmay comprise at least one subsection (e.g., n-type contacts 710). Thelaser treated semiconductor section 602 may be disposed between thep-type contacts 706. The substrate 704 may be n-type doped and includen-type contacts 710 on the same side of the substrate 704 as the lasertreated semiconductor section 702. The laser treated section 702 may besubstantially bounded by the p-type contacts 706. The p-type contacts706 may be substantially bounded by the n-type contacts 710. Byarranging the lateral diode configuration 700 such that the n-typecontacts 710 and the p-type contacts 706 are in close proximity, then-type 710 and p-type 706 layers will have a higher built in voltagethan the n-type 710 to laser treated semiconductor 702 and p-type 706 tolaser treated semiconductor-702 junctions. The high built-in voltagebetween the n-type 710 and p-type 706 layers allows the p-type 706 tolaser treated semiconductor 702 to n-type 710 conduction path todominate. The absorption of photons at the p-n junction will contributeto the lateral diode sensitivity. In some embodiments, to aid theabsorption of longer length photons, the p-n junction may not beshielded with an opaque material. In the above diode embodiments,reversing the doping of the n-type and p-type contacts and/or reversingthe Schottky metals may provide a similar functioning diode with areversed electron flow.

The present invention should not be considered limited to the particularembodiments described above, but rather should be understood to coverall aspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention may be applicable, will bereadily apparent to those skilled in the art to which the presentinvention is directed upon review of the present disclosure. The claimsare intended to cover such modifications.

What is claimed is:
 1. A photodiode device, comprising: a substrate; afirst doped section formed at a side of the substrate; a second dopedsection formed at an opposite side of the substrate from the first dopedsection; and a laser treated semiconductor section adjacent to and inelectrical contact with the first doped section such that the firstdoped region and the second doped region are positioned to generate anelectric field substantially capable of depleting at least a portion ofthe laser treated semiconductor section of free carriers and separatingresulting electron-hole pairs generated in the laser treatedsemiconductor section.
 2. The device of claim 1, further comprising: afirst contact coupled to the first doped section; and a second contactcoupled to the second doped section.
 3. The device of claim 1, whereinthe first doped section and the second doped section are substantiallyannular and the laser treated section is substantially disk shaped. 4.The device of claim 1, wherein the first doped section is n-doped andthe second doped section is p-doped.
 5. The device of claim 4, whereinthe laser treated semiconductor section includes a net doped n-typematerial and the n-doped first doped section has a higher level ofn-doping than the laser treated semiconductor section.
 6. The device ofclaim 1, wherein the laser treated semiconductor section includes amicro structured surface.
 7. The device of claim 1, wherein the firstdoped section is a plurality of first doped sections.
 8. The device ofclaim 7, wherein the plurality of first doped sections is located onmultiple sides of the laser treated semiconductor section.
 9. Aphotodiode device, comprising: a substrate; a first doped section formedat a side of the substrate; a second doped section formed at an oppositeside of the substrate from the first doped section; and amicrostructured surface adjacent to and in electrical contact with thefirst doped section such that the first doped region and the seconddoped region are positioned to generate an electric field substantiallycapable of separating electron-hole pairs generated in themicrostructured surface and moving resulting carriers to an appropriatecontact.
 10. The device of claim 9, further comprising: a first contactcoupled to the first doped section; and a second contact coupled to thesecond doped section.
 11. The device of claim 9, wherein the first dopedsection and the second doped section are substantially annular and themicrostructured surface is substantially disk shaped.
 12. The device ofclaim 9, wherein the first doped section is n-doped and the second dopedsection is p-doped.
 13. The device of claim 12, wherein themicrostructured surface includes a net doped n-type material and then-doped first doped section has a higher level of n-doping than themicrostructured surface.
 14. The device of claim 9, wherein themicrostructured surface is a short pulse laser modified surface.
 15. Thedevice of claim 14, wherein the short pulse laser modified surface ismodified with femtosecond laser pulses or picosecond laser pulses. 16.The device of claim 9, wherein the first doped section is a plurality offirst doped sections.
 17. The device of claim 16, wherein the pluralityof first doped sections is located on multiple sides of themicrostructured surface.